Some things I have done/seen done:
First, once you are past the first 24 hours, sewing up a wound is not a good idea. It's contaminated and the loose tissue, if any, is dead--which means it will harbor and protect bacterial infection in the wound if you use it to cover.
That means you are stuck with letting the wound heal 'by second intention', which means that the wound will heal from the edges inward, slowly. And it can be VERY slow!, so be patient.
If you have a vet in the area who is willing to work with chickens, I'd recommend a visit. They're unexpectedly tough birds, but sometimes a little help is needed for optimal healing to happen. Dead tissue really should be removed by a professional, but can be snipped away CAREFULLY to expose healthy pink tissue with good blood supply if you are SURE you know what you are doing. If you aren't sure, don't try it. As the wound heals, the dead tissue will become clear, and generally will come off fairly easily.
Keep encouraging her to eat--soft boiled/chopped, scrambled, hardboiled and crumbled, and mixed with a good quality chicken feed. Plenty of water--and you can put electrolytes/vitamins in that to help her along as well, just don't overdo it.
As for antibiotics...if the wound is dry and clean, or pink and moist without pus, I would not give them.
There are a couple of different ways to deal with large skinned wound areas--dry and moist healing/bandaging techniques. Twice-daily hot packing can be helpful (you use a warm moist washcloth on the area, which does two things--it softens crusts and scabs for careful removal, and it encourages circulation to the area). Something like the wound you describe is not something I would like to try dry-healing, so you'll need an ointment like neosporin, bacitracin, or similar which is safe for use in laying chickens. Slather on a reasonable amount, lay Telfa non-stick pads over it, then use a baby T shirt or similar to hold it all in place. Change every day to two days according to how it looks, and gradually, as the tissue heals, reduce the bandaging and ointment until healing is complete.
GOOD LUCK!
